Did Koro-sensei Really Say “The Master Has Failed More Times Than the Novice Has Tried”?
The English line is real: CBR prints it in body text under his name, and fans place it in season one, episode sixteen, after Karma fails the finals. But the sentence is older than the episode. Cartoonist Stephen McCranie published it in a comic in October 2012, two and a half years before the episode aired.
Yes, in English, and the sentence was not new when he said it. "The difference between the novice and the master is that the master has failed more times than the novice has tried" is printed under Koro-sensei's name by CBR and placed by fans in the first season's sixteenth episode. It is also, almost word for word, a line from a comic the American cartoonist Stephen McCranie published in October 2012, when Assassination Classroom was three months into serialization and the anime was more than two years away.
The verdict
From another work. Two dates settle the order. McCranie's comic essay "Be Friends with Failure" went up on his site Doodle Alley on 10 October 2012, and a copy archived in January 2013 already shows readers quoting the sentence back to him: "Do you want to know the difference between a master and a beginner? The master has failed more times than the beginner has even tried." Assassination Classroom's episode sixteen, "School's Out, 1st Term," first aired on 8 May 2015. The manga began in Weekly Shonen Jump in July 2012, but the first-term finals, where Karma coasts and loses, are well past the opening chapters and were published after McCranie's comic. Whichever way the borrowing ran, the English aphorism existed first, and the Assassination Classroom version is a rewording of it: "novice" for "beginner," "tried" for "even tried."
What is and is not established
What the record shows is the English. CBR's list of life lessons from the series prints the line in a sentence, credited to Koro Sensei, and Anime News Network's review of episode sixteen confirms the scene it belongs to: Karma decides he does not need to take the finals seriously, gets disappointing marks across the board, and the class E wins come from students nobody expected. What the record does not show is the Japanese. The fan catalogs of Koro-sensei's lines from that scene quote him telling Karma that a great talent grows most if it learns the sting of losing early, and calling him a brat brandishing a rusted blade; none of them has a sentence contrasting a master's failures with a novice's attempts. That leaves two possibilities. Either Yusei Matsui wrote a Japanese line close enough that the English localization reached for McCranie's phrasing, or the localization reached for it on its own. This page cannot tell those apart and does not try. What it can say is that the sentence as it circulates in English is McCranie's, reworded.
Why it travels under the octopus
Because it fits him better than it fits a comic about drawing. McCranie's comic is addressed to artists afraid of their own bad pages. Koro-sensei is a teacher whose whole method is letting students fail in front of him and then explaining what the failure was for, and the Karma episode is the clearest case in the series: a boy who has never lost at anything loses, and the lesson is the loss. Put the sentence in that mouth and it stops being advice and becomes a scene. That is why the Assassination Classroom version, not McCranie's, is the one that turns up on classroom posters now, and why Goodreads lists the sentence under McCranie while the anime quote lists file it under Koro-sensei. Both are right about their own version.
What to quote
Either, with the right name. If the point is the aphorism, it is McCranie's, from a 2012 comic. If the point is the scene, it is Koro-sensei's English line from episode sixteen, and it is fair to say so as long as the older source is not denied. Assassination Classroom does not have a hub on this site yet, because its sourcing is editorial only: there is no Wikiquote page for the series, and a hub built from listicle headings would not meet the standard the rest of the site holds to.
How we checked
The verification process asks for a primary or editorial source printing the line inside a sentence, which CBR does. The Doodle Alley post was read in an archived copy from January 2013, the air date comes from the episode list, and the Japanese fan catalogs were searched for the master-and-novice phrasing and did not have it. The entry in the fact-check database is filed as borrowed from another work. If a reader can supply the Japanese line from the episode or the chapter, the contact page is open and the page will say which way the borrowing ran.